find their currents flowing with a steady course, 

 though in some instances with great rapidity, plunging 

 over rocks and precipices, yet no alluvion or a grain 

 of sand is seen to disturb the pellucid streams. If a 

 rock, or an island obstruct its course, its current is 

 changed. If it should pass through a strait, or be con- 

 tracted by projecting points of land, its velocity is 

 increased, yet it is steady in its course. The same, 

 with some small difference, may be observed in the 

 currents of air, or wind. 



On the contrary, when, by the melting of snows or 

 the falling of rains, the waters rush in torrents into 

 the auxiliary branches, and thence by latteral courses 

 into the rivers, their currents are agitated, their 

 velocity increased, the sand and alluvions matter is 

 torn up and wafted away with their streams. 



If there be an island, or islands, or other obstruc- 

 tions in its course, they occasion a counter current, or 

 eddy at their lower extremity, where the current is 

 slackened, and the alluvion is deposited ; and where 

 there is an annual, and sometimes semi-annual recur- 

 rence of these causes, and repeated for ages, need we 

 wonder that shifting sand banks, bars, and islands, 

 should be formed in the beds of rivers ? However it 

 may be, the same results are produced by violent and 

 unsteady, or variable currents of the air, or winds. 



If the winds rush, in unsteady and violent gusts, 

 over the land, no matter from what quarter or point of 

 the compass, not only the dust but even the sand is 

 hurled into the air with the same facility as by a 



